With a bodylift it will push the shifter just enough to pop it out of gear. If you can give the shifter a little push and it works again this is your problem. What happens is the shifter boot on the trans bumps the boot of the tcase and pops it out of gear or in some cases the floor board needs to be trimmed to keep it from bumping it. The torque of the engine will cause the shifter to move into the floor board bumping out of gear. There is an extensive write up by someone around here on bodylifts and the things that could be an issue. This exact issue is addressed, I have a link to the thread at home and I'll post it if I can't find it. If you have a 2 inch bodylift just push the boot for the trans below the big lip of the stick and leave it there. If you have a 3 inch you will more than likely have to trim the opening.
